Devices, systems and methods for creation of a peripherally located fistula

ABSTRACT

Devices, systems and methods are disclosed for the formation of an arteriovenous fistula in the limb of the patient. Embodiments include a device for the creation, modification and maintenance of a fistula that includes an integral fistula creation assembly near its distal end that passes through the skin of the patient, through a first vessel such as an artery, and into a second vessel such as a vein. The fistula creation assembly preferably includes an anastomotic implant that is placed within the fistula to maintain long-term blood flow therethrough. The devices, systems and methods can be used to treat patients with one or more numerous ailments including chronic obstructive pulmonary disease, congestive heart failure, hypertension, hypotension, respiratory failure, pulmonary arterial hypertension, lung fibrosis and adult respiratory distress syndrome.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/946,454 (Attorney Docket No. 29919-706.301, now U.S. Pat. No.______), filed Nov. 28, 2007, which is a continuation ofPCT/US2006/024858 (Attorney Docket No. 29919-706.601), filed on Jun. 26,2006, which claims priority from U.S. Application No. 60/696,319(Attorney Docket No. 29919-706.101), filed on Jun. 30, 2005, the fulldisclosures of each which are incorporated herein by reference.

BACKGROUND Field of the Invention

The present invention relates generally to medical devices and methods.More particularly, the present invention relates to devices and methodsfor creating or modifying a fistula between a first vessel and a secondvessel, such as for the treatment of chronic obstructive pulmonarydisease.

Chronic obstructive pulmonary disease affects millions of patients inthe United States alone. The present standard of care is externallysupplied oxygen therapy, which requires a patient to remain near astationary oxygen source or carry a bulky oxygen source when away fromhome or a treatment facility. It is easy to appreciate that such oxygentherapy has many disadvantages.

Lung reduction surgery has recently been proposed for treating patientswith chronic pulmonary disease. Such surgery, however, is not a panacea.It can be used on only a small percentage of the total patientpopulation, requires long recovery times, and does not always provide aclear patient benefit. Even when successful, patients often continue torequire supplemental oxygen therapy.

There is therefore a need for improved approaches, including bothdevices and methods, for treating patients suffering from chronicobstructive pulmonary disease. If would be desirable if such devices andmethods were also useful for treating patients with other conditions,such as congestive heart failure, hypertension, lung fibrosis, adultrespiratory distress syndrome, and the like. Such devices and methodsshould provide for effective therapy, preferably eliminating the needfor supplemental oxygen therapy in the treatment of chronic obstructivepulmonary disease. There is a need for simplified devices and proceduralmethods that reduce costs to the patient and healthcare system, as wellas decrease procedure times and minimize patient risks. Improved devicesand procedures must be developed to apply to a broad base of patientpopulations with a wide range of applicable arteriovenous anatomies. Atleast some of these objectives will be met by the invention describedhereinafter.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the invention, a device for creating afistula in a patient is disclosed. The device comprises an elongatetubular structure comprising a proximal end and a distal end. The distalend is configured to penetrate or otherwise pass first through the skinof the patient, then through a first vessel, and then into a secondvessel. The device includes an integral assembly configured to create afistula between two neighboring vessels. In a preferred embodiment, thefirst vessel is an artery and the second vessel is a vein. In analternative, also preferred embodiment, the first vessel is a vein andthe second vessel is an artery. The fistula is typically created at alocation wherein the artery and vein vessel walls are within 20 mm ofeach other. The fistula is created to provide therapeutic benefit, suchas for an acute period less than twenty-four hours, a sub-chronic periodbetween twenty-four hours and thirty days, or for a chronic periodgreater than thirty days. The fistula creation assembly is preferablymounted on a core that is slidable within an outer sheath of the device.The fistula creation assembly can be uncovered from the sheath by anoperator through advancement of the core, retraction of the sheath, or acombination of the two movements. In a preferred embodiment, a secondslidable core, such as a slidable needle assembly with a sharpened,beveled tip, is slidingly received by the first core. When fullyadvanced, the needle assembly exits the distal end of both the sheathand the first core, and assists in penetrating first through the skin ofthe patient and then through the tissue that exists along the trajectoryto the proposed fistula. Both the first core and the sheath preferablyhave tapered ends to assist in penetration and/or advancement throughthe skin and tissue up to the fistula site. In another preferredembodiment, the needle assembly includes a guidewire lumen for insertionof a guidewire from outside the patient's body, through the first vesseland into the lumen of the second vessel. In another embodiment, theneedle assembly is removable. In a preferred embodiment, the device isrigid along a majority of its length. In an alternative embodiment, thedevice is flexible along a majority of its length, such as a flexiblesection that can be advanced down a segment of the first vessel prior toentering the second vessel. In another alternative embodiment, thedevice includes both flexible segments and rigid segments along itslength.

The fistula creation assembly of the present invention can be configuredin numerous forms to produce the desired fistula. In a preferredembodiment, a cone shaped dilator is expanded and/or delivers energy tocreate the fistula. In another embodiment, an expandable balloon is usedto create the fistula. An anastomotic implant is preferably deployed toinitially create the fistula and/or to improve the long-term patency ofthe fistula. The implant can perform numerous functions, and may includeself-expanding materials, plastically deformable materials, or acombination of self-expanding or plastically deformable materials. In apreferred embodiment, the anastomotic implant forms the fistula into anoval cross section. In an alternative embodiment, the anastomoticimplant forms the fistula into a circular cross section. Numerous formsof energy can be used to create and/or improve the fistula, includingenergies selected from the group consisting of: electrical energy suchas radiofrequency or microwave energy; cryogenic energy; heat;radiation; chemical energy; light such as light delivered tophotoreactive agents; and combinations thereof. The fistula creationassembly may deliver an agent to the fistula and its surrounding tissue,such agents selected from the group consisting of: anti-proliferative;anti-biotic; anti-thrombogenic; and combinations thereof.

In a preferred embodiment, the device is configured to create a fistulato treat a patient suffering from COPD, such as via the fistuladecreasing systemic vascular resistance of the patient. In these andother patient populations, the fistula may provide therapy by increasingthe oxygen content of venous blood, such as blood supplied to a lung ofthe patient. The fistula may additionally cause oxygen content inarterial blood to also increase. The fistulas of the present inventionare configured to have blood flow through the fistula of at least 5ml/min, and preferably greater than 50 ml/min.

In yet another preferred embodiment, the device includes a handle at itsproximal end. The handle includes one or more controls, such as controlsto advance and/or retract a slidable core. In a preferred embodiment,one or more controls are included to perform a function selected fromthe group consisting of: initiate or modify the delivery of energy to anintended or existing fistula location; expand a distal portion of thedevice such as an expandable dilator or inflatable balloon; deploy animplant such as an anastomotic device which applies tension between thetwo vessels at the fistula location and/or scaffolds the lumen of thefistula; and combinations thereof.

In yet another preferred embodiment, the device is configured to createa fistula in a limb of a patient, such as between an artery and veinselected from the group consisting of: axillary artery; brachial artery;ulnar artery; radial artery; profundal artery; femoral artery; iliacartery; popliteal artery; carotid artery; saphenous vein; femoral vein;iliac vein; popliteal vein; brachial vein; basilic vein; cephalic vein;medial forearm vein; medial cubital vein; axillary vein; and jugularvein. In an alternative embodiment, the fistula is located in theabdomen or thorax of the patient.

In yet another preferred embodiment, the fistula creation device furthercomprises a flow measurement element, such as an ultrasound or Dopplerultrasound element, or a lumen that allows a flow measurement catheterto be inserted into the proximal end of the device and advanced to alocation near or beyond the device's distal end. Flow measurement can bemade directly using Doppler technologies and techniques, or indirectlyby measuring flow channel geometries.

In yet another preferred embodiment, the fistula creation device furthercomprises flow adjustment means mounted to one or more of the outersheath or an inner core. The flow adjustment means can be activated ondemand by an operator and preferably includes: an energy deliveryelement; an agent delivery element; an inflatable balloon; an expandabledilator; a deployable implant such as a second implant of the fistulacreation device; and combinations thereof.

According to a second aspect of the invention, a system for creating afistula is disclosed. The system includes one or more of the embodimentsof the fistula creation device of the first aspect of the invention, andan ultrasound visualization monitor. The visualization monitor may beconfigured to display information received from one or more ultrasoundcrystals integral to the fistula creation device, or may work withseparate device such as an external or internal ultrasound probe.

According to a third aspect of the invention, a system for creating afistula is disclosed. The system includes one or more of the embodimentsof the fistula creation device of the first aspect of the invention, andan apparatus selected from the group consisting of: a balloon catheter;an anastomotic implant deployment catheter; a flow measurement devicesuch as a flow catheter or an external Doppler probe; an angiographycatheter; a venography catheter; a guidewire; an introducer; a needle; abiopsy needle; and combinations thereof. In a preferred embodiment, thesystem further comprises an ultrasound visualization monitor configuredto provide an image received from one or more of: an ultrasound elementintegral to the fistula creation device; an external ultrasound probe;and an internal ultrasound apparatus such as an intravascular ultrasoundcatheter; and an inserted probe such as a transesophageal probe.

According to a fourth aspect of the invention, a method of creating afistula is disclosed. The distal end of a fistula creation device isplaced through the skin of the patient. The distal end, which ispreferably the distal end of a sharpened, beveled tip needle assembly,such as a removable needle assembly, is advanced through a first vessel,such as a vein or an artery. The distal end is then advanced into asecond vessel at an existing-fistula or an intended-fistula location. Afistula is then created, or an existing fistula is maintained, such thata long-term flow of blood is provided between the first vessel and thesecond vessel. The fistula creation device includes an elongate tubularstructure that may be rigid along a majority of its length, may beflexible along a majority of its length, or may include rigid andflexible portions such as two rigid portions attached with a flexiblehinge. In a preferred embodiment, blood flows from the first vessel tothe second vessel. In an alternative, also preferred embodiment, bloodflows from the second vessel to the first vessel. At the intendedfistula location of the patient, the vessels may lie in variousgeometric configurations, such as wherein the first vessel is “on top”of the second vessel such that the lumen of the first vessel liesrelatively proximate the shortest line between the lumen of the secondvessel at the fistula location and the surface of the patient's skin. Inalternative fistula locations, the vessels may lie in a more“side-to-side” configuration. When inserted, the elongate body of thefistula creation device is positioned to lie relatively in the planedefined by the lumens of the two vessels near the intended fistulalocation. While maintaining position within this plane, the fistulacreation device can be inserted at an angle relatively perpendicular tothe surface of the patient's skin, or at a smaller angle, such as anangle between 20 and 80 degrees. This insertion angle may be chosen bythe clinician to affect the fistula angular geometry between the twovessels, such as at a small insertion angle to correspond to a similarlysmall angle between the lumen of the first vessel and the lumen of thefistula. Such a small angle between the first vessel lumen and thefistula lumen may be desirous to reduce turbulent flow through thefistula. In alternative embodiments, an insertion angle approximatingninety degrees may be chosen in order to minimize the length of thefistula.

In a preferred embodiment, the method further comprises the step ofdetermining the anatomical location for the fistula. Prior to creatingthe fistula, the fistula location is determined using one or more of:angiography; venography; extra-vascular ultrasound; intravascularultrasound; Doppler ultrasound; and MRI. The fistula location isdetermined based on an analysis of a parameter selected from the groupconsisting of: first vessel diameter; second vessel diameter; arterydiameter; vein diameter; ratio of artery to vein diameter; distancebetween the artery and vein lumens; geometric relationship between theartery and vein lumens; distance from an arterial side branch; distancefrom an venous side branch; arterial flow; venous flow; oxygen contentin artery; oxygen content in vein; wall thickness of artery; wallthickness of vein; degree of calcification of artery; degree ofcalcification of vein; geometric relationship between the artery andvein lumens at the fistula site; hemodynamic factors; other parameters;and combinations thereof.

In another preferred embodiment, the method further comprises the stepof performing a blood flow measurement procedure, such as a procedureperformed prior to fistula creation, during fistula creation, afterfistula creation, and combinations thereof. The information determinedduring the flow measurement procedure can be used to select the fistulasite, modify the fistula such as a balloon dilation fistula modificationprocedure and/or otherwise treat the fistula.

In yet another preferred embodiment, an anastomotic implant is placed inthe fistula. The anastomotic implant is placed to provide a functionselected from the group consisting of: scaffolding an opening betweenthe first vessel and the second vessel; reducing neointimalproliferation into the fistula flow path; preventing tissue fromprotruding into the fistula flow path; placing a portion of the firstvessel wall in tension with the tissue of the second vessel wall;reducing bleeding of the tissue neighboring the fistula; enhancinghealing of the tissue neighboring the fistula; and combinations thereof.The anastomotic implant may include one or more coatings, such asanti-bacterial; anti-thrombogenic and anti-prolific coatings. Theanastomotic implant may additionally or alternatively include a coveredportion, such as a partial covering, such covering materials selectedfrom the group consisting of: polytetrafluoroethylene; Dacron; Nitinol;stainless steel; and combinations thereof. The fistula creation deviceof the present invention preferably places the anastomotic implant.

In yet another preferred embodiment, a guidewire is placed between thefirst and second vessel through the fistula, prior to, during, or afterthe fistula is created. The guidewire preferably remains in place afterthe fistula creation device is removed, or partially removed, such thata second catheter device can be placed over that guidewire. The secondcatheter device can be used to perform a diagnostic event such as aradiographic dye injection catheter inserted to perform angiography orvenography, or an ultrasound catheter used to visualize the fistulastructure. The second catheter device can be used to modify the fistulasuch as a balloon catheter inserted to enlarge the fistula or ananastomotic implant deployment catheter inserted to increase or decreaseflow through the fistula.

In yet another preferred embodiment, the fistula is created to providetherapeutic benefit that results from: a decrease is systemic vascularresistance; an increase in the oxygen content in at least a portion ofthe venous system such as the venous supply to a lung of the patient;and combinations thereof. Blood flow through the fistula is at least 5ml/min and preferably greater than 50 ml/min. The fistula is preferablycreated between an artery and a vein at a location in a limb of thepatient. The artery is selected from the group consisting of: axillaryartery; brachial artery; ulnar artery; radial artery; profundal artery;femoral artery; iliac artery; popliteal artery; and carotid artery. Thevein is selected from the group consisting of: saphenous; femoral;iliac; popliteal; brachial; basilic; cephalic; medial forearm; medialcubital; axillary; and jugular. The artery is preferably between 5 mmand 25 mm in diameter at the intended fistula location. The vein ispreferably less than 35 mm in diameter at the intended fistula location.The fistula preferably has a non-circular or oval cross section, suchthat the major axis of the oval is greater than either the vein diameteror the artery diameter. In an alternative embodiment, the fistula has acircular cross section. The geometry of the cross section of the fistulais preferably matched with a similar geometry of an anastomotic implantplaced during the disclosed method.

According to a fifth aspect of the invention, a kit for creating along-term fistula in a patient for the treatment of COPD is disclosed.The kit includes a first fistula creation device for forming a fistulawith a first geometry. The kit further includes a second fistulacreation device for forming a fistula with a second geometry. Either thefirst or the second fistula creation device is used to create thelong-term fistula based on an analysis of information gathered during avisualization procedure performed on the patient. The visualizationprocedure is preferably selected from the group consisting of:ultrasound visualization including intravascular ultrasound andextravascular ultrasound; angiography; venography; MRI; and combinationsthereof. The first fistula creation device and the second fistulacreation device can be configured to create a first fistula and a secondfistula respectively. The first fistula and the second fistula may havetwo different cross sectional geometries, such as a circular and an ovalcross sections, two different circular cross sections or two differentoval cross sections. Varied oval cross sections may include ovals withdifferent major axes and different minor axes, and ovals with differentmajor axes with similar minor axes.

Both the foregoing general description and the following detaileddescription are exemplary and are intended to provide furtherexplanation of the embodiments of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate various embodiments of thepresent invention, and, together with the description, serve to explainthe principles of the invention. In the drawings:

FIG. 1 illustrates a partial cross sectional side view of a fistulacreation apparatus consisting with the present invention;

FIG. 2 a illustrates a cross sectional side view of a fistula creationapparatus consistent with the present invention shown with a slidableneedle assembly in the advanced position;

FIG. 2 b illustrates the fistula creation apparatus of FIG. 2 a with theneedle assembly removed;

FIG. 2 c illustrates the fistula creation apparatus of FIG. 2 b with anouter sheath retracted such that an integral anastomotic implant ispartially expanded;

FIG. 2 d illustrates the fistula creation apparatus of FIG. 2 c with theouter sheath further retracted such that the integral anastomoticimplant is fully expanded;

FIG. 3 a is a cross sectional side view of a device and method forcreating a fistula consistent with the present invention shown prior toadvancement of the device through the patient's skin;

FIG. 3 b illustrates the device and method of FIG. 3 a shown with thedistal end of a slidable needle assembly of the device having penetratedthe skin and the first wall of an artery;

FIG. 3 c illustrates the device and method of FIG. 3 b shown with theneedle assembly having further penetrated a second wall of the arteryand a first wall of a vein, and a guidewire having been advanced downthe vein through a lumen of the needle assembly;

FIG. 3 d illustrates the device and method of FIG. 3 c shown with theneedle assembly having been retracted while leaving the guidewire seatedin the vein;

FIG. 3 e illustrates the device and method of FIG. 3 d shown with ananastomotic implant of the device partially deployed in the vein;

FIG. 3 f illustrates the device and method of FIG. 3 e shown with theanastomotic implant of the device fully deployed in the fistula betweenthe artery and the vein, and the device outer sheath partially retractedfrom the patient;

FIG. 4 a is a cross sectional side view of a device and method forcreating a fistula consistent with the present invention shown withadvancement of the distal end of the device through the patient's skinand into an artery and an ultrasound probe located proximate the entrysite;

FIG. 4 b illustrates the ultrasound image produced by the ultrasoundprobe of FIG. 4 a.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the present embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 1 depicts a preferred embodiment of the fistula creation device ofthe present invention. Device 10 is configured to be inserted by anoperator through the skin of a patient to create and/or maintain afistula that provides a flow of blood between a first vessel and asecond vessel, such as a long-term flow of blood to achieve atherapeutic benefit. Device 10 includes an elongate tubular structurewith a proximal end and a distal end, the tubular structure comprisingmultiple tubes that surround or are slidingly received within a separatetube. Each tube may have a rigid, semi-rigid, and/or flexibleconstruction and each tube comprises one or more materials such as:nylon; polyvinyl chloride; polyethylene; polypropylene; polyimide;Pebax™; Hytrel™; polyurethane; silicone; steel; Nitinol™; blends, alloysand copolymers of the preceding, or other biocompatible materials, andmay include a structural braid such as a nylon or metal braid commonlyused in interventional guide catheters. Each tube may include a tapered,sharpened, beveled, expandable such as balloon expandable, and/or energyemitting distal end, and each tube may include one or more lumens, suchas a Teflon-lined or Teflon-coated lumen. The elongate tubular structuremay be rigid or flexible along a majority of its length, or may includeboth rigid and flexible portions such as two rigid portions separated bya flexible hinge portion. Device 10 further includes, on its proximalend, handle 40, which is grasped by an operator to advance, retract,rotate, control, activate, and/or otherwise manipulate device 10 or acomponent or sub-assembly of device 10. Each advanceable and/orretractable tube of device 10 may be attached at its proximal end to oneor more advancement and/or retraction controls, such as a tube that isoperably attached to a control integral to or proximate to handle 40.Handle 40 may include additional controls, such as a control to enlargea dilator, inflate a balloon, deploy an implant, initiate energy oragent delivery, activate a diagnostic device and/or perform anotherfunction.

The outermost tube, outer sheath 30, which preferably has a tapereddistal end and is constructed of a biocompatible plastic, surrounds andslidingly receives a first slidable core, inner core 20, which includesconically tapered tip 21 and is preferably constructed of biocompatiblemetal and/or plastic. Fistula creation assembly 25 is mounted near thedistal end of inner core 20 and is configured to create a fistula ondemand by an operator. Fistula creation assembly 25 may include one ormore of various means to create the fistula such as a cone shapeddilator, not shown, such as a dilator that is expandable and/orconfigured to deliver energy. Fistula creation assembly 25 may include aforce-exerting balloon, such as a compliant or non-compliant balloonand/or a balloon to dilate an implant. Alternatively or additionally,fistula creation assembly 25 may include a delivery assembly and ananastomotic implant, such as a vessel-to-vessel tensioning anastomoticclip and/or a fistula scaffolding assembly. Alternatively oradditionally, fistula creation assembly 25 may include an energydelivery element such as an element configured to deliver electricalenergy such as radiofrequency or microwave energy; cryogenic energy;heat; radiation; chemical energy; light; and/or other forms of energy.Energy may be delivered to ablate tissue, cut tissue and/or coagulateblood and tissue. Alternatively or additionally, fistula creationassembly 25 may include an agent delivery assembly, such as an agentdelivery mechanism configured to deliver one or more ofanti-proliferatives; anti-biotics; and anti-thrombogenics. In apreferred embodiment, fistula creation assembly 25 further is configuredto modify an existing fistula, such as a fistula created by device 10previously used to create the fistula, or by a separate device 10 or analternative fistula creation device, such as during the same medicalprocedure or a previously performed procedure. In order to modify anexisting fistula, fistula creation assembly 25 may include ananastomotic implant, such as a second anastomotic implant nested withina first implant, an expandable balloon, an energy or agent deliveryelement, a tissue removing element such as a forward or pull backatherectomy catheter, or other means. Other fistula modifying events canbe performed such as the placement of an implant, which partially coversthe fistula from either the venous or arterial side.

Referring back to FIG. 1, fistula creation assembly 25 is operablyattached to conduit 26, a flexible or rigid conduit which travelsproximally to handle 40. Conduit 26 may include one or more of: a poweror data transfer conduit such as one or more electrical wires and/oroptical fibers, a tube such as an inflation lumen or cryogenic flowtube; and a slidable cable such as a pull wire. Conduit 26 iselectrically attached through an electrical switch control, button 42,to another control on handle 40, port 41. Port 41 is an electrical jackthat can be attached to an energy delivery unit such as an RF generator,not shown. An operator depresses button 42 to deliver energy to fistulacreation assembly 25. In an alternative or additional embodiment, port41 is attached to a balloon endoflator that is used to inflate a balloonintegral to fistula creation assembly 25. In another alternative oradditional embodiment, port 41 is attached to a drug delivery pump orsupply to deliver drugs to fistula creation assembly 25. Outer sheath 30is operably attached to a control on handle 40, sheath retraction knob32, which can be slid proximally by an operator to retract outer sheath30 and subsequently slid distally to advance outer sheath 30. Outersheath 30 is retracted to expose fistula creation assembly 25, such aswhen fistula creation assembly 25 is an expandable balloon and/or ananastomotic implant delivery assembly such as an assembly including aself-expanding anastomotic implant. In an alternative embodiment, innercore 20 is advanced to expose fistula creation assembly 25, or acombination of advancing inner core 20 and retracting outer sheath 30 isperformed. Inner core 20 is operably attached to core advancement knob22 of handle 40 such that inner core 20 can be advanced and retracted bysliding core advancement knob 22 forward or back.

Located in the distal portion of inner core 20 and in proximity tofistula creation element 25 is visualization element 70, preferably anultrasound element such as a phased array of ultrasound crystals, signaland power wires not shown, or a rotating ultrasound crystal, rotatingshaft and signal and power wires not shown. Visualization element 70 canbe electrically connected to an ultrasound monitor, not shown, such thata cross sectional view of the tissue and other structures surroundingthe distal portion of device 10 and fistula creation assembly 25 can bevisualized. In alternative embodiments, visualization element 70consists of a visualization marker, such as an ultrasonically reflectivesurface that can be visualized with an external ultrasound probe, aradiopaque marker that can be visualized under fluoroscopy, a magneticmarker, and other markers compatible with visualization equipment foundin hospitals, doctor's offices and other health care settings. Anoperator utilizes visualization element 70 during various proceduralsteps involving device 10, such as penetration of its distal end throughthe skin and vessels of the patient and rotational orientation of thedevice. Visualization element 70 also provides valuable informationprior to, during, and after the activation of fistula creation element25 such as information relating to the inflation of a balloon and/orplacement of an anastomotic implant. In an alternative embodiment,device 10 further includes a flow measurement element, not shown,preferably embedded in visualization element 70, such as a Dopplerultrasound function. In another alternative embodiment, a visualizationcatheter or flow measurement catheter is inserted in a lumen of device10, such as within the lumen of inner core 20 in which needle assembly50 is inserted, a separate lumen of inner core 20 not shown, or a lumenof outer sheath 30. In a preferred embodiment, device 10 furtherincludes a visualization and/or flow measurement monitor, such as aDoppler ultrasound monitor.

A second slidable core, needle assembly 50, is slidingly received withina lumen of inner core 20. Needle assembly 50, which may be rigid orflexible along its length, is preferably constructed of one or moremetals such as stainless steel and Nitinol. Needle assembly 50 can beretracted, and completely removed from the lumen of inner core 20 byretraction of yet another control of handle 40, needle retraction knob52. In an alternative embodiment, full removal of needle assembly 50 isprevented by the inclusion of one or more mechanical stops. Needleassembly 50 has a sharpened distal tip 51, which is preferably sharp andbeveled. Needle assembly 50 includes a lumen from its proximal end toits distal end, guidewire lumen 53, which is configured to allow astandard interventional guidewire to be advanced therethrough, andfurther configured to allow needle assembly 50 to be removed leaving thepreviously inserted guidewire to reside within the lumen of inner core20 previously inhabited by needle assembly 50. In an alternativeembodiment, needle tip 51 may be configured to deliver energy, such asRF energy used to assist in advancement, and/or to cauterize, cut andablate tissue.

In a preferred embodiment, a kit is provided for the creation ofmultiple fistulas, in a single patient or multiple patients, includesmultiple fistula creation devices of FIG. 1 with varied fistula creationelements in each device. An operator selects a specific fistula creationdevice based on the configuration of the fistula creation elementincluded in that device. In one alternative, a first fistula creationdevice creates a fistula with a different geometry than a second fistulacreation device, such as might be chosen to differentiate a fistulabetween vessels with a first set of luminal diameters and a second setof fistulas with different luminal diameters. Numerous fistula creationparameters can be varied between a first fistula creation device and asecond fistula creation device such as use of energy, fistula diameter,fistula cross section geometry such as circular cross section versuselliptical cross section wherein the major diameter of the ellipse is atleast 20 percent larger than the minor diameter of the ellipse. In apreferred embodiment, the major diameter of the fistula is at leasttwice the minor diameter. In another preferred embodiment, a kitincludes a first fistula creation device with a target fistula crosssection dimensions having unequal major and minor axes, and a secondfistula creation device with a target fistula cross section dimensionshave similar minor axis length and greater major axis length. In apreferred method, an operator selects either the first fistula creationdevice or the second fistula creation device based on a visualizationprocedure performed on the anatomy of the patient proximate the intendedfistula creation site.

Referring now to FIGS. 2 a through 2 d, a preferred embodiment of afistula creation device of the present invention is shown in variousstages of a preferred method of activation. Referring specifically toFIG. 2 a, device 10 is configured to be inserted by an operator throughthe skin of a patient to create and/or maintain a fistula that providesa flow of blood between a first vessel and a second vessel, such as along-term flow of blood to achieve a therapeutic benefit. Device 10includes an elongate tubular structure with a proximal end and a distalend, the tubular structure comprising multiple tubes that surround orare slidingly received within a separate tube. Each tube may have arigid, semi-rigid, and/or flexible construction and each tube comprisesone or more materials such as: nylon; polyvinyl chloride; polyethylene;polypropylene; polyimide; Pebax™; Hytrel™; polyurethane; silicone;steel; Nitinol™; blends, alloys and copolymers of the preceding, orother biocompatible materials, and may include a structural braid suchas a nylon or metal braid commonly used in interventional guidecatheters.

The outermost tube, outer sheath 30, which preferably has a tapereddistal end, surrounds and slidingly receives a first slidable core,inner core 20, which includes conically tapered tip 21. Outer sheath 30includes on its proximal end sheath advancement knob 32, which ismanipulated by an operator to advance and retract outer sheath 30. Innercore 20 includes on its proximal end, core advancement knob 22, which ismanipulated by an operator to advance and retract inner core 20. Balloon25 is mounted near the distal end of inner core 20 and is expandable ondemand by an operator, inflation lumen and endoflator attachment portnot shown, such as to create the fistula and/or expand an implant placedto maintain the fistula. Balloon 25 may comprise a compliant ornon-compliant balloon. Surrounding balloon 25 is an anastomotic implant,clip 60, which is deployed in the fistula to perform one or morefunctions including but not limited to: scaffolding an opening betweenthe first vessel and the second vessel; reducing neointimalproliferation into the fistula flow path; preventing tissue fromprotruding into the fistula flow path; placing a portion of the firstvessel wall in tension with the tissue of the second vessel wall; andreducing bleeding of the tissue neighboring the fistula; enhancinghealing of the tissue neighboring the fistula. In a preferredembodiment, the anastomotic implant includes an active agent, such as ananti-thrombogenic or anti-proliferative agent, and may also include acovering or partial covering.

A second slidable core, needle assembly 50, is slidingly received withina lumen of inner core 20. Needle assembly 50, which may be rigid orflexible along its length, is preferably constructed of one or moremetals such as stainless steel and Nitinol. Needle assembly 50 can beretracted, and completely removed from the lumen of inner core 20 byretraction of needle retraction knob 52. In a preferred embodiment,Inner core 20 can also be retracted, and completely removed from thelumen of outer sheath 30, by retraction of knob 20. Needle assembly 50has a sharpened distal tip 51, which is preferably sharp and beveled.Needle assembly 50 includes a lumen from its proximal end to its distalend, guidewire lumen 53, which is configured to allow a standardinterventional guidewire to be advanced therethrough, and furtherconfigured to allow needle assembly 50 to be removed leaving thepreviously inserted guidewire to reside within the lumen of inner core20 previously inhabited by needle assembly 50. In an alternativeembodiment, needle assembly 50 is partially retracted but remains withinlumen of inner core 20. In another alternative embodiment, needle tip 51may be configured to deliver energy, such as RF energy used to assist inadvancement, and/or to cauterize, cut and ablate tissue. In a preferredmethod, device 10 is advanced through the skin, through a first vesseland into the lumen of a second vessel with needle assembly 50 in thefully advanced position. A locking mechanism, not shown, may be engagedto prevent relative motion between needle assembly 50 and outer sheath30 during insertion and subsequent advancement. A guidewire is thenadvanced through guidewire lumen 53 and further advanced down the lumenof the second vessel.

Referring now to FIG. 2 b, needle assembly 50 has been completelyremoved from the lumen of inner core 20, such as when a guidewire hasbeen successfully placed from a location outside the patient's skin toand into the second vessel. Referring now to FIG. 2 c, the distal end ofclip 60 has been released from being constrained by outer sheath 30,either by retraction of outer sheath 30, advancement of inner core 20,or a combination of both movements. Clip 60 of FIGS. 2 a through 2 d isself-expanding, such as a resiliently biased tubular structure made ofNitinol. In FIG. 2 d, clip 60 has been fully released from beingconstrained and is in a fully expanded condition. Balloon 25 has beeninflated, inflation lumen and endoflator attachment not shown, toprovide additional expansion force to clip 60. In an alternativeembodiment, clip 60 is plastically deformable, or includes plasticallydeformable portions, such that balloon 25 is required to expand clip 60.In a preferred embodiment, device 10 of FIGS. 2 a through 2 d is used asa system in conjunction with one or more additional devices to createand/or maintain the fistula. Such additional devices include but are notlimited to guidewires and various over-the-wire devices that are placedover the guidewire placed through needle assembly 50, after needleassembly 50 is removed. These additional over-the-wire devices may beplaced within a lumen of inner core 20, within a lumen of outer sheath30 with inner core 20 removed, or over the guidewire after device 10 hasbeen completely removed. These over-the-wire devices include but are notlimited to: balloon catheters; anastomotic implant delivery devices andimplants; flow measurement catheters; angiography catheters; venographycatheters; and other over-the wire devices applicable to modifying thefistula, such as modifying the flow of the fistula, or to perform aprocedure to otherwise enhance and/or maintain the long term benefit ofthe fistula.

Referring now to FIGS. 3 a through 3 f, a preferred method of using thefistula creation device of the present invention is shown. A crosssectional view of a patient's anatomy at a proposed fistula location 111is depicted wherein artery 130 is directly above vein 120 in relation toskin surface 105. Intended fistula location 111 may be determined usingone or more visualization techniques including but not limited to:angiography; venography; extra-vascular ultrasound; intravascularultrasound; and MRI. Intended fistula location 111 may be determinedusing one or more flow measurement techniques such as Dopplerultrasound. The intended fistula location 111 may be selected based onparameters selected from the group consisting of: first vessel diameter;second vessel diameter; artery diameter; vein diameter; ratio of arteryto vein diameter; distance between the artery and vein lumens; geometricrelationship between the artery and vein lumens; distance from anarterial side branch; distance from an venous side branch; arterialflow; venous flow; oxygen content in artery; oxygen content in vein;wall thickness of artery; wall thickness of vein; degree ofcalcification of artery; degree of calcification of vein; geometricrelationship between the artery and vein lumens at the fistula site;hemodynamic factors; other parameters; and combinations thereof.

Artery 130 includes, in closest proximity to skin 105, arterial wall131. Vein 120 includes, in closest proximity to artery 130, venous wall121. At the intended fistula location 111 of the patient, the vesselsmay lie in various geometric configurations, such as the geometry ofFIGS. 3 a through 3 f wherein the first vessel is relatively “on top” ofthe second vessel such that the lumen of the first vessel liesrelatively proximate the shortest line between the lumen of the secondvessel at the fistula location and the surface of the patient's skin. Inalternative fistula locations, the vessels may lie in a more“side-to-side” configuration. When inserted, the elongate body of outersheath 30 is positioned to lie relatively in the plane defined by thelumens of the two vessels near the intended fistula location. Whilemaintaining position within this plane, the fistula creation device canbe inserted at an angle relatively perpendicular to the surface of thepatient's skin, or at a smaller angle as is shown in FIG. 3 a, such asan angle between 20 and 80 degrees. This insertion angle may be chosenby the clinician to form the resultant fistula angular geometry betweenthe two vessels, such as at a small insertion angle to correspond to asimilarly small angle between the lumen of the first vessel and thelumen of the fistula. Such a small angle between the first vessel lumenand the fistula lumen may be desirous to reduce turbulent flow throughthe fistula. In alternative embodiments, an insertion angleapproximating ninety degrees may be chosen, such as to minimize thelength of the resultant fistula. Vein 120 is preferably a vein locatedin a limb of the patient, such as a vein selected from the groupconsisting of: saphenous vein; femoral vein; iliac vein; popliteal vein;brachial vein; basilic vein; cephalic vein; medial forearm vein; medialcubital vein; axillary vein; and jugular vein. Artery 130 is preferablyan artery in a limb of the patient, such as an artery selected from thegroup consisting of: axillary artery; brachial artery; ulnar artery;radial artery; profundal artery; femoral artery; iliac artery; poplitealartery; carotid artery.

Referring now specifically to FIG. 3 a, a fistula creation device ispositioned with its distal end near an intended skin puncture site andincludes outer sheath 30 with distal end 31. Outer sheath 30 ispreferably constructed of a biocompatible catheter material, suchmaterials and construction methods described in detail hereabove.Extending beyond distal end 31 is the distal end of a slidable needleassembly including needle tip 51 and guidewire lumen 53. The needleassembly is preferably constructed of a metal or metal alloy such asstainless steel or Nitinol, and needle tip 51 is a sharpened, beveledtip.

Referring now to FIG. 3 b, needle tip 51 has been advanced through skin105, through artery wall 31, and into the lumen of artery 130. Distalend 31 of outer sheath 30 has also passed through skin 105 without anysignificant displacement between needle tip 51 and distal end 31, eitherby a releasable fixation device, not shown but integral to the fistulacreation device, or by stabilization of both the outer sheath 30 and theneedle assembly by the operator. Referring now to FIG. 3 c, needle tip51 has been advanced out of artery 130, through venous wall 121 and intothe lumen of vein 120. Similar to the advancement shown in FIG. 3 b,there has been no relative displacement between needle tip 51 and distalend 31 of outer sheath 30, such that distal end 31 has also advancedinto the lumen of vein 120. Guidewire 80 has been advanced from theproximal end of the fistula creation device, through guidewire lumen 53and down the lumen of vein 120. Referring now to FIG. 3 d, the needleassembly has been retracted such needle tip 51 has moved proximal toouter sheath 30 distal end 31, while leaving guidewire 80 deep seatedinto vein 120.

Referring now to FIG. 3 e, a self-expanding anastomotic implant, clip60, is partially deployed out of distal end 31 of outer sheath 30, suchthat two tensioning arms 61 and two stabilizing arms 62 have beenreleased from being constrained within outer sheath 30. Clip 60 has beenpartially deployed through one or more actions including: pushing clip60 out of outer sheath 30 via advancement of a core contained withinouter sheath 30; retracting sheath 30 such as while maintaining thelongitudinal position of clip 60; or by a combination of these twoactions. While clip 60 is partially deployed, the fistula creationdevice is retracted to a position wherein one or more of tensioning arms61 are in firm contact with venous wall 121, position not shown. Clip 60is then fully deployed such as by retraction of sheath 30, advancementof clip 60, or a combination of the two actions. Referring now to FIG. 3f, clip 60 has been fully deployed such that fistula 110 is scaffoldedby clip 60, the four tensioning arms 61 placing vein 120 and artery 130in tension at a location neighboring fistula 110, and stabilization arms62 stabilizing clip 60 in the vessels to prevent twisting or other clip60 migrations. Clip 60 is preferably configured such that fistula 110has an oval cross-section, with a major axis at least twenty percentgreater than the minor axis of the oval. In a preferred embodiment, themajor axis has a diameter larger than either vein 120 or artery 130'sluminal diameter. In an alternative embodiment, clip 60's constructiongeometry causes fistula 110 to have a circular cross section.

Shown in FIG. 3 f, the fistula creation device is being withdrawn, suchthat distal end 31 of outer sheath 30 is almost removed from enteringskin 105. Guidewire 80 remains in place, such that one or moreadditional devices can be placed over-the-wire and easily access eitherthe artery 130 or venous 120 side of fistula 110. These subsequentover-the-wire devices, described in detail in reference to FIG. 2 d, canbe used to assess the fistula such as an ultrasound catheter tovisualize the fistula, or a Doppler ultrasound catheter to measurefistula flow. The over-the-wire devices can be used to modify thefistula such as to modify the flow rate through the fistula, or tootherwise improve the therapeutic benefit of the fistula such as toincrease the long-term patency of the fistula or to minimize adverseside effects of the fistula. In a preferred embodiment, an over-the-wireor other procedure is performed to measure flow through the fistula. Ifinadequate flow is determined, a flow modification procedure may beperformed, such as an over-the-wire flow modification procedureutilizing an inflatable balloon or a tissue removing device to increasefistula flow. In a preferred embodiment, the inflatable balloon has anon-circular geometry which corresponds to a fistula created with anon-circular geometry. The balloon may be integral to the fistulacreation device, or a separate over-the-wire catheter, and may beinflated to apply force to clip 60, or a second implant, all not shown.Other flow modification procedure may also be performed, such asprocedures which place implants, within or external to the flow path, toincrease or decrease fistula flow to maximize therapeutic benefit and/orreduce adverse side effects. Other flow modification procedures that maybe performed include application of an agent such as an anti-biotic,anti-thrombogenic or anti-proliferative agent, or delivery of energysuch as radiation delivery to prevent neointimal growth.

The method and device of FIGS. 3 a through 3 f are used to create afistula for therapeutic benefit such as to treat a patient with COPD.The fistula can be created for various purposes such as: increasing theoxygen content of venous blood supplying a lung of the patient, increasethe oxygen content of arterial blood; and/or decreasing systemicvascular resistance. The fistula can be created for an acute period lessthan twenty-four hours, a sub-chronic period between twenty-four hoursand thirty days, as well as for a chronic period longer than thirtydays. The fistula preferably provides a flow of blood from the arterialsystem to the venous system of greater than 5 ml/min, typically greaterthan 50 ml/min. Clip 60 provides one or more functions including but notlimited to: scaffolding an opening between the first vessel and thesecond vessel; reducing neointimal proliferation into the fistula flowpath; preventing tissue from protruding into the fistula flow path;placing a portion of the first vessel wall in tension with the tissue ofthe second vessel wall; reducing bleeding of the tissue neighboring thefistula; enhancing healing of the tissue neighboring the fistula; andcombinations thereof. While clip 60 has been described as aself-expanding device such as a resiliently biased Nitinol component,anastomotic implants that are plastically deformable or include bothself-expanding sections and balloon expandable portions are alsopreferred. In an alternative embodiment, clip 60 includes a covering,such as a covering that surrounds the interior of the tissue within thefistula between the artery and vein lumens. The covering is abiocompatible material such as polytetrafluoroethylene; Dacron; Nitinol;stainless steel; or combinations thereof. In another alternativeembodiment, clip 60 includes an agent, such as an agent that is eludedover time including anti-bacterial, anti-thrombogenic and/oranti-prolific agents. While, the method of FIGS. 3 a through 3 fillustrate an artery to vein connection method, a vein to arteryapproach is also a preferred method of this invention.

The device and method of FIGS. 3 a through 3 f create an initialpuncture through the skin of the patient, subsequently penetrating intoand through the first vessel, and into the lumen of the second vessel.In an alternative, also preferred embodiment, not shown, a standardvessel introducer and sheath is utilized, making the initial puncturethrough the skin of the patient and into the first vessel. The fistulacreation device distal end is then inserted into the sheath, passingthrough the skin and into the first vessel. The fistula creation devicedistal end exits the end of the sheath and further exits the lumen ofthe first vessel at the intended fistula location site by penetratingthrough the first vessel wall, and enters the lumen of the second vesselby penetrating through the second vessel wall. The intended fistulalocation may be proximate the site that the vessel introducer enteredthe first vessel, or at a location remote from this site, such as at alocation greater than 20 mm from the first vessel entry site. Fistulasmay be created remote from the first vessel entry site by intraluminallyadvancing the introducer sheath and/or the fistula creation device downthe lumen of the first vessel prior to the distal end of the fistulacreation device exiting the first vessel lumen and penetrating into thesecond vessel.

Referring now to FIGS. 4 a and 4 b, a method and system for creating afistula is shown in which an operator utilizes a fistula creation deviceand ultrasound visualization system in combination. A cross sectionalview of a patient's anatomy at a proposed fistula location 111 isdepicted wherein artery 130 is directly above vein 120 in relation toskin surface 105. Intended fistula location 111 may be determined usingone or more visualization techniques including but not limited to:angiography; venography; extra-vascular ultrasound; intravascularultrasound; and MRI. Intended fistula location 111 may be determinedusing one or more flow measurement techniques such as Dopplerultrasound. The intended fistula location 111 may be selected based onparameters selected from the group consisting of: first vessel diameter;second vessel diameter; artery diameter; vein diameter; ratio of arteryto vein diameter; distance between the artery and vein lumens; geometricrelationship between the artery and vein lumens; distance from anarterial side branch; distance from an venous side branch; arterialflow; venous flow; oxygen content in artery; oxygen content in vein;wall thickness of artery; wall thickness of vein; degree ofcalcification of artery; degree of calcification of vein; geometricrelationship between the artery and vein lumens at the fistula site;hemodynamic factors; other parameters; and combinations thereof.

Artery 130 includes, in closest proximity to skin 105, arterial wall131. Vein 120 includes, in closest proximity to artery 130, venous wall121. While vein 120 and artery 130 are shown in a line relativelyperpendicular to skin 105, adjusting the orientation of outer sheath 30can not only vary insertion angles, but also accommodate anatomies withvessels in a relatively side-by-side configuration (relativelyequidistant from skin surface 105) as has been described hereabove inreference to FIGS. 3 a through 3 f. In a preferred method, the fistulacreation device enters the skin at an angle relatively perpendicular toskin 105. In another preferred embodiment, the fistula creation devicepenetrated the skin at an angle between 20 and 80 degrees relative tothe surface of the skin 105. Vein 120 is preferably a vein located in alimb of the patient, such as a vein selected from the group consistingof: saphenous vein; femoral vein; iliac vein; popliteal vein; brachialvein; basilic vein; cephalic vein; medial forearm vein; medial cubitalvein; axillary vein; and jugular vein. Artery 130 is preferably anartery in a limb of the patient, such as an artery selected from thegroup consisting of: axillary artery; brachial artery; ulnar artery;radial artery; profundal artery; femoral artery; iliac artery; poplitealartery; carotid artery.

Referring now to specifically to FIG. 4 a, a fistula creation device ispositioned with its distal end at an intended fistula site 111. Thefistula creation device includes outer sheath 30, which is preferablyconstructed of a biocompatible catheter material, such materials andconstruction methods described in detail hereabove. Extending beyonddistal end 31 of outer sheath 30 is the distal end of a slidable needleassembly including needle tip 51 and guidewire lumen 53. The needleassembly is preferably constructed of a metal or metal alloy such asstainless steel or Nitinol, and needle tip 51 is a sharpened, beveledtip. Needle tip 51 has been advanced through skin 105, through arterywall 31, and into the lumen of artery 130 residing near intended fistulasite 111. Distal end 31 of outer sheath 30 has also passed through skin105 without any significant displacement between needle tip 51 anddistal end 31, either by a releasable fixation device, not shown butintegral to the fistula creation device, or by stabilization of both theouter sheath 30 and the needle assembly by the operator.

Also shown in FIG. 4 a is ultrasound probe 71, which is positionedrelatively orthogonal to the surface of skin 105, and preferably held byan operator, operator not shown, to provide a visual cross sectionalimage of intended fistula site 111, as well as artery 130, vein 120, andany devices crossing through the imaging plane of ultrasound probe 71.Ultrasonic coupling gel 74, common to external ultrasound probe use, isfirst placed on the skin, in the area to be visualized, to enhance theimage produced by ultrasound probe 71 via improved acoustic couplingbetween ultrasound probe 71 and skin 105. Referring additionally to FIG.4 b, ultrasound probe 71 is attached to an ultrasound generator, notshown, as well as ultrasound monitor 72 which displays on imaging area73 the cross sectional image associated with the imaging plane of FIG. 4a. Manipulation of probe 71, either in the position of contact with skin105 and/or the relative angle made with the surface of skin 105,modifies the location of the imaging plane and the associated imagedisplayed on monitor 72. Ultrasound probe 71 and monitor 72 are used andmanipulated by an operator as a system including the fistula creationdevice of the present invention. This system is used to assess andpre-determine the location of intended fistula location 111. Thevisualization equipment is also used to view and confirm advancements ofthe percutaneous devices such as catheter, sheath, inner tube andguidewire advancements; confirm device locations such as device distalend (tip) locations; and assist in other preferred fistula creationsteps of the present invention in which real-time visualization of theprocedure can be made available to an operator. In an alternative, alsopreferred embodiment, as an alternative to or in conjunction withultrasound probe 71, an internal ultrasound probe provides an image tomonitor 72. The internal probe, not shown, is selected from the groupconsisting of: an ultrasound catheter such as a rotational or phasedarray intravascular ultrasound catheter; an inserted probe such as atransesophageal probe; and combinations thereof.

In subsequent steps, not shown but similar to steps 3 c through 3 fhereabove, needle tip 51 will be advanced out of artery 130, throughvenous wall 121 and into the lumen of vein 120. A guidewire, not shown,will be advanced from the proximal end of the fistula creation device,through guidewire lumen 53 and down the lumen of vein 120. The needleassembly will then be retracted such that needle tip 51 will beretracted proximal to distal end 31 of outer sheath 30, while leavingthe guidewire deep seated into vein 120. An anastomotic implant, notshown, is deployed such as by retraction of sheath 30 while maintainingthe position of the anastomotic implant. The anastomotic implant isconfigured such that the resultant fistula has an oval cross-section,with a major axis at least twenty percent greater than the minor axis ofthe oval. The fistula creation device is then withdrawn, such thatdistal end 31 of outer sheath 30 is almost removed from entering skin105. The guidewire preferably remains in place, such as through astandard vessel introducer, not shown. In a preferred embodiment, outersheath 30 performs as the vessel introducer. Leaving the guidewire inplace allows one or more additional devices to be placed over-the-wireand easily access either the venous or arterial side of the fistula.These subsequent over-the-wire devices, described in detail in referenceto FIG. 2 d, can be used to assess the fistula such as an ultrasoundcatheter to visualize the fistula, or a Doppler ultrasound catheter tomeasure fistula flow. The over-the-wire devices can be used to modifythe fistula such as to modify the flow rate through the fistula, or tootherwise improve the therapeutic benefit of the fistula such as toincrease the long-term patency of the fistula or to minimize adverseside effects of the fistula. In a preferred embodiment, an over-the-wireor other procedure is performed to measure flow through the fistula. Ifinadequate flow is determined, a flow modification procedure may beperformed, such as an over-the-wire flow modification procedureutilizing an inflatable balloon or a tissue-removing device to increasefistula flow. In a preferred embodiment, the inflatable balloon has anon-circular geometry that corresponds to a fistula created with anon-circular geometry. The balloon may be integral to the fistulacreation device, or a separate over-the-wire catheter, and may beinflated to apply force to clip 60, or a second implant, all not shown.Other flow modification procedure may also be performed, such asprocedures that place implants, within or external to the flow path, toincrease or decrease fistula flow to maximize therapeutic benefit and/orreduce adverse side effects.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A method for percutaneously creating a fistulabetween a patient's artery and vein, said method comprising: providingan assembly comprising a sheath having lumen therethrough and a needleremovably received in the sheath, wherein the needle has a needle tipconfigured to be advanced through tissue; percutaneously advancing theassembly through a skin layer of the patient and between a lumen of theartery and a lumen of the vein; advancing a guidewire through a lumen ofthe needle and outwardly from the needle tip; retracting the needleproximally over the guidewire while the sheath remains in place; anddeploying a clip over the guidewire to scaffold the fistula between theartery and the vein.
 2. A method as in claim 1, wherein the artery islocated above the vein in relation to the skin surface.
 3. A method asin claim 1, further comprising determining the fistula location prior toadvancing the assembly through the skin layer.
 4. A method as in claim3, wherein determining the fistula location comprises one or morevisualization techniques selected from angiography, venography,extra-vascular ultrasound, intravascular ultrasound, and MRI.
 5. Amethod as in claim 3, wherein determining the fistula location comprisesDoppler ultrasound.
 6. A method as in claim 1, wherein the assembly isinserted at an angle in the range from 20° to 80° relative to anexternal surface of the skin layer.
 7. A method as in claim 1, whereinthe assembly is inserted at an angle approximately 90° relative to anexternal surface of the skin layer.
 8. A method as in claim 1, whereinthe artery and the vein are peripheral.
 9. A method as in claim 1,wherein percutaneously advancing the assembly comprises advancing theneedle tip through the skin layer, through the artery and into the veinso that the needle tip is in a lumen of the vein.
 10. A method as inclaim 9, wherein the guidewire is advanced into the venous lumen priorto retracting the needle.
 11. A method as in claim 10, wherein deployingthe clip comprises partially advancing the clip from a distal end of thesheath to release one or more tensioning arms on the clip.
 12. A methodas in claim 11, further comprising retracting the sheath to contact thetensioning arm(s) against the venous wall prior to fully deploying theclip.
 13. A method as in claim 12 wherein fully deploying the clipengages two tensioning arms against the venous wall and two tensioningarms against an arterial wall.
 14. A method as in claim 1, wherein thefistula has an oval cross-section.
 15. A method as in claim 14, whereinthe oval has a major axis which is at least 20% greater than a minoraxis.
 16. A method as in claim 15, wherein a length of the major axis islarger than a diameter of the vein or artery.
 17. A method as in claim1, further comprising introducing a catheter over the guidewire afterthe clip has been deployed.
 18. A method as in claim 17, wherein thecatheter is introduced to perform at least one of visualize the fistula,measure fistula flow, or modify the fistula.
 19. A method as in claim 1,further comprising selecting a patient suffering from at least one ofchronic obstructive pulmonary disease, congestive heart failure,hypertension, hypotension, respiratory failure, pulmonary arterialhypertension, lung fibrosis and adult respiratory distress syndrome.